How come we've never met before?
CO-me MAI non ci SIA-mo MAI in-con-TRA-ti PRI-ma — stress on 'co-', 'mai', 'sia-', 'tra-', 'pri-'. The double 'mai' adds rhythmic emphasis.
Classic flirtatious line — expresses that meeting this person feels significant and that you wish it had happened sooner.
'Come mai' = how come. 'Non ci siamo mai incontrati' = we have never met (passato prossimo of the reflexive 'incontrarsi'). 'Prima' = before. The use of 'mai' twice in the sentence is not a mistake — 'come mai' and 'non... mai' serve different grammatical roles.
Dove eri finora?
Where have you been all this time?
More poetic — implies you were waiting without knowing it
Sembra impossibile non averti incontrato prima.
It seems impossible not to have met you before.
Gentler and more reflective — wonder rather than complaint
Mi chiedo come mai le nostre strade non si siano incrociate prima.
I wonder how our paths never crossed before.
Elegant — 'le strade si incrociano' is a beautiful Italian metaphor for meeting
Italian flirting often has a philosophical edge — connecting romantic attraction to ideas of fate, timing, and meaning. This kind of flirtation is considered sophisticated and is particularly effective with educated, culturally curious Italians.